Justus von liebig



UNITED STATES PATENT OFFICE.

JUSTUS VON LIEBIG, 0F MUNICH, BAVARIA.

.IMPROVEMENT IN ELECTROPLATING WITH COPPER AND OTHER METALS THE ,SILVEREDSURFACES 0F. MIRRORS AND OTHER ARTICLES FOR PROTECTING THE SAME.

Specification forming part of Letters Patent No. 38,721, dated November 12, 1861.

or silvered surfaces-such as glass mirrors and other articles of silvered glass-by means of the use in the galvauo-plastic process of a neutral solution of the double salt tartrate of oxide of 'copper and soda (potash or ammo; nia) or an alkaline solution of gold, nickel, tin, or other metals, which may be prepared for use as hereinafter described.

One important practicalfu'se of my inven. tion is, as before stated, the coating of the silvered surface of glass mirrors or other articles of glass with a film of metallic copper, thereby efl'ectually protecting it from abrasion and in- I am aware of course that the depositing of one metal upon another by means of the galvano-plastic process is not new as a general thing, and that the coating of articlesof copper with silver by this means is well known; but the coating of silver or silvered surfaces with copper has not been accomplished prior to my invention, and cannot be done by any known process of electroplatin gotherwise than by .means of the solutions the use of which for this purpose 1 claim as my invention.

In order to enable others skilledin the art to make use of my invention, Iwill proceed to describe its practical application to the coating of the silvered surface of a glass mirror with a film of copper, which is efl'ected in the following manner:

A glass plate, one surface of which has already been covered with a reflecting-film of silverby any of the known processes for that purpose, is placed horizontallyor vertically in a tub or vessel made of gutta-percha, wood lined with caoutchouc, or other suitable material, and in the same tub, at the distance bf about half an inch from the silvered surface of the glass plate,- a sheet of copper of the same dimensions as the glass plate is also fixed. The

tub is now filled with the solution of the salt of copper, nickel, or gold, hereinafter described, and the silver coating of the glass plate is brought in contact by means of a motallic wire or conductor with the negative pole or zine end,of a voltaic battery, while the copperplate is brought .in contact similarly with the positive pole or copper end of the same voltaic battery. A battery such as that of Bunsen, consisting of one or more voltaic couples, according to the dimensions of the silver surface to be coated, may be employed to advantage.' So soon as the connection with the battery is made, as just described, the silver film on the glass becomes covered immediately by a coating of copper; but the glass plate should remain in the solution from ten to twenty-five minutes, according to the thickness of coating required. The silver surface of the mirror is effectually protected by the coating of copper thus applied from the tarnishin g effect or action of the sulphureted hydrogen in the air, as well as from injury by mechanical abrasion.

Theprocess which I have described is equally applicable to .other than plane surfaces, and with precisely similar effect, and also to the depositing of gold, nickel, or tin by substituting an alkaline solution of a salt of either of those metals for the solution of copper.

I will now proceed to describe the mode of preparing the metallic solutions used in my process.

The neutral solution of copper which I. use is prepared by dissolving twenty-five (25) parts of sulphate of copper in one hundred (100) parts of water, adding a solution of twenty-eight (28) parts of the double tartrate of soda and potash (commonly called iRochellesaltW in the same quantity of water, which suffices to precipitate the oxide of copper the form of tartrate, and afterward adding. caustic soda, potash, or ammonia in such proportions as to redissolve the precipitate. To one volume of this solution, which ought to be, perfectly neutral, is added an equal volume of water.

The alkaline gold solution is prepared by dissolving one part of the double chloride of gold and sodium in one hundred and twenty (120) parts of water and adding to that solution two (2) parts of caustic soda. The alkaline solution of nickel is prepared by adding aslight excess of ammonia to a solution of one part of sulphate of nickel in forty (40) parts of water.

I am aware that various plans have been proposed for protecting the silvered surfaces of looking-glasses-as, for example, the application of a coat or coats of varnish or paint for that purpose. I therefore do not claim broadly the protecting of the silvered surfaces of glass mirrors by the application of a coating of some other substance; neither do I claim the use of the electrotype process, nor the use therein of the common salts of copper, which possess an acid reaction, or cyanurets, which cannot be practically employed to ad vantage; but

What I do claim as my invention, and desire to secure by Letters Patent, is-

1. The use,in the galvano-plastic process of depositing upon silver or silv'ered surfaces gold, copper, or nickle, or other metals, of the neutral solutions of the metal to be deposited prepared with the double tartrate of soda, potash, or ammonia in-the manner substantially as horeinhefore described.

2. The mode hereinbefore described of coating the silvered surfaces of glass mirrors or other articles with a metallic film of gold, copper, nickel, or other metals by the use in the electroplating process of the neutral solution of copper and the alkaline solutions of other metals in the manner substantially as hereinbefore set forth.

JUS'I US VON LIEBlG. 

